This invention relates to improvements in quick-mount side shifters for mounting load-handling attachments on the carriage of a forklift truck.
The use of side shifters interposed structurally between a conventional lift truck load carriage and a load-handling attachment, to enable selective transverse shifting of the load-handling attachment relative to the lift truck carriage, is well-known. Usually the installation of such side shifters requires substantial time and effort on the part of the lift truck dealer or user, primarily due to the requirement for welding an anchor to the carriage of the lift truck to which is attached one end of the side shifter's hydraulic ram assembly. Such welded anchors are shown, for example, in U.S. Pat. Nos. 3,460,700 and 4,165,008 respectively. Some lift trucks can accommodate the placement of the side shifter hydraulic ram assembly in a position between the upper and lower attachment mounting bars of the carriage as shown in the aforementioned U.S. Pat. No. 4,165,008, which position is desirable because of the protection for the ram assembly afforded thereby. However other forklift trucks may have structures or components which interfere with the placement of the ram assembly in this area, and in such cases an upper placement of the ram assembly, above the upper attachment mounting bar as shown in U.S. Pat. No. 3,460,700, is required. The person installing the side shifter must be aware of these potential problems and exercise appropriate care in the location and orientation of the ram assembly anchor prior to welding it to the lift truck carriage. Moreover, after such anchor has been properly attached to the carriage, friction-reducing bushings or shoes must be mounted on the top of the upper attachment mounting bar of the carriage, the side shifter mounted on the carriage and the side shifter's hydrulic ram connected to the aforementioned ram anchor, all of which is time-consuming. In addition, in applications such as lift truck rental fleets, the side shifter may need to be repeatedly demounted for replacement by other load-handling attachments, depending upon the particular needs of the users, which is also a time-consuming process.
To solve the aforementioned mounting and demounting difficulties with side shifters, several types of "quick-mount" side shifters have been developed in the past. One of these is shown in British patent application publication No. 2,030,542, and features a quick-mounting anchor bracket which attaches to the upper attachment mounting bar of the lift truck carriage in substantially the same removable manner that a lift truck attachment would, and without the need for any welding. Such quick-mounting anchor bracket engages the upper teeth of the mounting bar so as to resist transverse motion with respect thereto, and the side shifter's sliding frame is supportably and slidably mounted atop the anchor bracket by means of an elongate, downwardly-opening hook or guide, with a friction-reducing bushing or shoe interposed between the anchor bracket and hook to facilitate relative sliding between the side shifter frame and the anchor bracket. Other quick-mount side shifters, used principally in Europe, have been sold under the trademarks CASCADE, TECTOR, BOLZONI, MEYER, KAUP and MANDIGERS respectively.
Most of these prior quick-mount side shifters recognize the desirability of locating the side shifter hydraulic ram assembly in a position below the upper attachment mounting bar of the carriage so as to protect the ram assembly. However, in recognition of the interference problems posed by placement of the ram assembly in such location on some lift trucks, such side shifters generally provide a substantial forward clearance between the front of the lift truck carriage and the front of the side shifter to provide sufficient room for the ram assembly in any lift truck upon which the side shifter might be mounted. Unfortunately this approach tends to maximize the distance by which the front of the side shifter, and therefore the load-handling attachment, protrudes forwardly of the front axle of a counterbalanced lift truck, thereby tending to reduce the load-carrying capacity of the lift truck which is a serious disadvantage.
The most economical and reliable slide structure utilized by previous quick-mount side shifters is of the general type shown in the aforementioned British patent application publication, wherein the side shifter frame utilizes a downwardly-opening hook which fits supportably and slidably over the top of the anchor bracket with a friction-reducing bushing therebetween. The problem with most of such structures in the past has been that there is no way to keep the anchor bracket, friction-reducing bushing and side shifter frame in a fully-assembled condition when the side shifter is not mounted on a lift track carriage. This problem necessitates preassembly of the side shifter by the installer prior to mounting, detracting from the hoped-for facility of installation which is the objective of such a structure. One previous structure, a CASCADE quick-mount side shifter, utilizes a quick-mounting anchor bracket which extends substantially the full vertical height of the side shifter frame. Because of its substantial vertical dimension, such anchor bracket is prevented from disassembly from the side shifter frame, even in an unmounted condition, by means of removable connectors connecting the bottom of the anchor bracket to the bottom of the side shifter frame. However the substantial vertical dimension of the anchor bracket tends to maximize the forward protrusion of the side shifter, thereby detracting from the load-carrying capacity of the lift truck. Certain other types of previous quick-mount side shifters, such as the Kaup and Mandigers side shifters, do not utilize the economical and reliable downwardly-opening hook-type slide structure previously described, and therefore are not faced with the problem of preventing disassembly of the anchor bracket from the side shifter frame when the side shifter is not mounted on the carriage.
Another common problem of previous side shifters employing the downwardly-opening hook-type slide structure is that the moment imposed on the slide structure by the weight of the load tends to cause the friction-reducing bushing or shoe beneath the hook to ride upwardly with respect to its underlying support, thereby causing the bushing ultimately to be displaced from its proper position with resultant malfunction of the bushing and damage thereto. Although, in the past, such bushings have included retainer structures for preventing the bushings from being displaced transversely in the direction of the sliding motion, no structure has been provided to retain such bushings positively against upward displacement, and thus the aforementioned problem has remained.
In the use of previous quick-mount side shifters, particularly in connection with lift truck rental fleets where rapid demounting of a side shifter to accommodate the needs of the next user may be required, there has usually been some problem with respect to how to quickly and easily arrange some elevated support for the side shifter and its attachment so that the lift truck carriage may be detached and lowered from under the side shifter. Usually it is necessary to search for blocks of wood or similar supports to hold the side shifter a spaced distance above the ground in order to accomplish this. No means integral to a quick-mount side shifter have previously been provided for this purpose.
In addition, a previous problem with all side shifters, whether of the quick-mount or more conventional type, has existed with respect to the lower hook assemblies which slidably attach the bottom of the side shifter frame to the lower attachment mounting bar of the lift truck carriage. Proper vertical adjustment of these lower hooks is critical, because if they are too tight they will resist the transverse sliding motion necessary for proper operation of the side shifter, and if too loose they can become disengaged causing inadvertent detachment of the side shifter from the lift truck carriage resulting in injury to a load or to nearby workmen. An improvement in the fineness of the adjustability of the lower hook assembly is therefore needed for all side shifters.